ext4: Remove CONFIG_EXT4_FS_XATTR

Ted has sent out a RFC about removing this feature. Eric and Jan
confirmed that both RedHat and SUSE enable this feature in all their
product.  David also said that "As far as I know, it's enabled in all
Android kernels that use ext4."  So it seems OK for us.

And what's more, as inline data depends its implementation on xattr,
and to be frank, I don't run any test again inline data enabled while
xattr disabled.  So I think we should add inline data and remove this
config option in the same release.

[ The savings if you disable CONFIG_EXT4_FS_XATTR is only 27k, which
  isn't much in the grand scheme of things.  Since no one seems to be
  testing this configuration except for some automated compile farms, on
  balance we are better removing this config option, and so that it is
  effectively always enabled. -- tytso ]

Cc: David Brown <davidb@codeaurora.org>
Cc: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -848,7 +848,6 @@ struct ext4_inode_info {
 #endif
 	unsigned long	i_flags;
 
-#ifdef CONFIG_EXT4_FS_XATTR
 	/*
 	 * Extended attributes can be read independently of the main file
 	 * data. Taking i_mutex even when reading would cause contention
@@ -857,7 +856,6 @@ struct ext4_inode_info {
 	 * EAs.
 	 */
 	struct rw_semaphore xattr_sem;
-#endif
 
 	struct list_head i_orphan;	/* unlinked but open inodes */